Synthesized-beam RFID reader system with gain compensation and unactivated antenna element coupling suppression

ABSTRACT

A synthesized-beam transceiver system steers a beam of a two-dimensional antenna array by activating a first subset of antenna elements to orient the beam in a first direction and subsequently activating a second subset of the antenna elements to orient the beam in a different direction. The system also electrically connects antenna elements that are inactive, not in the first subset, or not in the second subset to a reference potential of the array.

BACKGROUND

Radio-Frequency Identification (RFID) systems typically include RFIDreaders, also known as RFID reader/writers or RFID interrogators, andRFID tags. RFID systems can be used in many ways for locating andidentifying objects to which the tags are attached. RFID systems areparticularly useful in product-related and service-related industriesfor tracking objects being processed, inventoried, or handled. In suchcases, an RFID tag is usually attached to an individual item, or to itspackage.

In principle, RFID techniques entail using an RFID reader to interrogateone or more RFID tags. The reader transmitting a Radio Frequency (RF)wave performs the interrogation. The RF wave is typicallyelectromagnetic, at least in the far field. The RF wave can also bepredominantly electric or magnetic in the near field. The RF wave mayencode one or more commands that instruct the tags to perform one ormore actions.

A tag that senses the interrogating RF wave may respond by transmittingback another RF wave. The tag either itself generates the other RF wave,or forms the wave by reflecting back a portion of the interrogating RFwave in a process known as backscatter. Backscatter may take place in anumber of ways.

The backscattered RF wave may encode data stored in the tag, such as anumber. The response is demodulated and decoded by the reader, whichthereby identifies, counts, or otherwise interacts with the associateditem. The decoded data can denote a serial number, a price, a date, atime, a destination, an encrypted message, an electronic signature,other attribute(s), any combination of attributes, and any othersuitable data. Accordingly, when a reader receives tag data it can learnabout the tag and/or the item that hosts the tag.

An RFID tag typically includes an antenna system, a radio section, apower management section, and frequently a logical section, a memory, orboth. In some RFID tags the logical section may include a cryptographicalgorithm which relies on one or more passwords or keys stored in tagmemory. In earlier RFID tags the power management section included anenergy storage device such as a battery. RFID tags with an energystorage device are known as battery-assisted, semi-active, or activetags. Advances in semiconductor technology have miniaturized theelectronics so much that an RFID tag can be powered solely by the RFsignal it receives. Such RFID tags do not include an energy storagedevice and are called passive tags. Of course, even passive tagstypically include temporary energy- and data/flag-storage elements suchas capacitors or inductors.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended asan aid in determining the scope of the claimed subject matter.

Synthesized-beam antennas (SBAs) use multiple antenna elements togenerate radio frequency (RF) radiation patterns with varying shapes andorientations. These radiation patterns can be used to receive ortransmit signals in particular directions. However, in some cases,radiation patterns oriented in different directions may have differentpower. For example, a radiation pattern oriented in a particulardirection may have higher power than a radiation pattern oriented in adifferent direction. Since the effectiveness of many antennaapplications is directly related to the power of the generated radiationpattern, having radiation patterns with reduced power may beundesirable.

Some embodiments are directed to methods and systems for steering a beamof a two-dimensional antenna array by activating or driving a firstsubset of antenna elements to orient the beam in a first direction,electrically connecting at least one antenna element not in the firstsubset to a reference potential of the antenna array, and subsequentlyactivating or driving a second subset of the antenna elements to orientthe beam in a second direction different from the first and electricallyconnecting at least one antenna element not in the second subset to thereference potential.

Other embodiments are directed to methods and systems for providing aconducted power to a two-dimensional antenna array to generate a beamwith a first radiated peak power at a first location, and in response tothe beam being directed to a second location, adjusting the conductedpower such that a second radiated peak power at the second location issubstantially the same as the first radiated peak power.

These and other features and advantages will be apparent from a readingof the following detailed description and a review of the associateddrawings. It is to be understood that both the foregoing generaldescription and the following detailed description are explanatory onlyand are not restrictive of aspects as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Detailed Description proceeds with reference to theaccompanying drawings, in which:

FIG. 1 is a block diagram of components of an RFID system.

FIG. 2 is a diagram showing components of a passive RFID tag, such as atag that can be used in the system of FIG. 1.

FIG. 3 is a conceptual diagram for explaining a half-duplex mode ofcommunication between the components of the RFID system of FIG. 1.

FIG. 4 is a block diagram showing a detail of an RFID reader, such asthe one shown in FIG. 1.

FIG. 9 depicts a synthesized-beam antenna according to embodiments.

FIGS. 10A and 10B depict potential beams that can be formed by thesynthesized-beam antenna of FIG. 9, according to embodiments.

FIG. 11 depicts a synthesized-beam transceiver system with a fixed-powertransceiver according to embodiments.

FIG. 12 depicts a synthesized-beam transceiver system capable ofcompensating for beam gain variations according to embodiments.

FIG. 13 is a block diagram of an RFID synthesized-beam reader systemaccording to one embodiment.

FIG. 14 is a block diagram of an RFID synthesized-beam reader systemaccording to another embodiment.

FIG. 15 is a flowchart depicting a synthesized-beam gain compensationprocess according to embodiments.

FIG. 16 depicts beam pattern variations in a synthesized-beamtransceiver system due to coupling with floating antenna elements.

FIG. 17 is a block diagram of a synthesized-beam antenna steering systemaccording to embodiments.

FIGS. 18A-C are block diagrams depicting details of synthesized-beamantenna termination systems according to embodiments.

FIG. 19 is a flowchart depicting a synthesized-beam antenna steeringprocess according to embodiments.

DETAILED DESCRIPTION

In the following detailed description, references are made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration specific embodiments or examples. These embodimentsor examples may be combined, other aspects may be utilized, andstructural changes may be made without departing from the spirit orscope of the present disclosure. The following detailed description istherefore not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims and theirequivalents.

Embodiments are directed to a synthesized-beam antenna transceiversystem that can compensate for beam gain degradation due to undesiredcoupling with radiation pattern side lobes and/or floating antennaelements. The transceiver system may compensate for beam gaindegradations by varying the conducted power provided to the antennaelements based on stored or sensed transmit power data and/orterminating unused antenna elements to a reference potential.

FIG. 1 is a diagram showing components of a typical RFID system 100,incorporating embodiments. An RFID reader 110 transmits an interrogatingRF wave 112. RFID tag 120 in the vicinity of reader 110 may senseinterrogating RF wave 112 and generate wave 126 in response. RFID reader110 senses and interprets wave 126.

Reader 110 and tag 120 communicate via waves 112 and 126. Whilecommunicating, each encodes, modulates, and transmits data to the other,and each receives, demodulates, and decodes data from the other. Thedata can be modulated onto, and demodulated from, RF waveforms. The RFwaveforms are typically in a suitable range of frequencies, such asthose near 900 MHz, 13.56 MHz, and so on.

The communication between reader and tag uses symbols, also called RFIDsymbols. A symbol can be a delimiter, a calibration symbol, and so on.Symbols can be implemented for exchanging binary data, such as “0” and“1” if desired. When the symbols are processed internally by reader 110and tag 120 they can be treated as values, numbers, and so on.

Tag 120 can be a passive tag, or an active or battery-assisted tag(i.e., having its own power source). When tag 120 is a passive tag it ispowered from wave 112.

FIG. 2 is a diagram of an RFID tag 220, which may be similar to tag 120of FIG. 1. Tag 220 is implemented as a passive tag, meaning it does nothave its own power source. Much of what is described in this document,however, applies also to active and battery-assisted tags.

Tag 220 is formed on a substantially planar inlay 222, which can be madein many ways known in the art. Tag 220 includes an electrical circuitwhich is preferably implemented as an integrated circuit (IC) 224. Insome embodiments, IC 224 may be implemented in complementary metal-oxidesemiconductor (CMOS) technology. In other embodiments IC 224 may beimplemented in other semiconductor technologies, such as bipolarjunction transistor (BJT) technology, metal-semiconductor field-effecttransistor (MESFET) technology, and others as will be well known tothose skilled in the art. IC 224 is arranged on inlay 222.

Tag 220 also includes an antenna for exchanging wireless signals withits environment. The antenna is often flat and attached to inlay 222. IC224 is electrically coupled to the antenna via suitable antenna contacts(not shown in FIG. 2).

IC 224 is shown with a single antenna port, comprising two antennacontacts electrically coupled to two antenna segments 227 which areshown here forming a dipole. Many other embodiments are possible usingany number of ports, contacts, antennas, and/or antenna segments.

In operation, the antenna receives a signal and communicates it to IC224, which both harvests power and responds if appropriate, based on theincoming signal and the IC's internal state. If IC 224 uses backscattermodulation then it responds by modulating the antenna's reflectance,which generates response wave 126 from wave 112 transmitted by thereader. Coupling and uncoupling the antenna terminals of IC 224 canmodulate the antenna's reflectance, as can a variety of other means.

In the embodiment of FIG. 2, antenna segments 227 are separate from IC224. In other embodiments, antenna segments may alternatively be formedon IC 224. Tag antennas according to embodiments may be designed in anyform and are not limited to dipoles. For example, the tag antenna may bea patch, a slot, a loop, a coil, a horn, a spiral, or any other suitableantenna.

The components of the RFID system of FIG. 1 may communicate with eachother in any number of modes. One such mode is called full duplex.Another such mode is called half-duplex, and is described below.

FIG. 3 is a conceptual diagram 300 for explaining the half-duplex modeof communication between the components of the RFID system of FIG. 1,especially when tag 120 is implemented as passive tag 220 of FIG. 2. Theexplanation is made with reference to a TIME axis, and also to a humanmetaphor of “talking” and “listening”. The actual technicalimplementations for “talking” and “listening” are now described.

RFID reader 110 and RFID tag 120 talk and listen to each other by takingturns. As seen on axis TIME, when reader 110 talks to tag 120 thecommunication session is designated as “R→T”, and when tag 120 talks toreader 110 the communication session is designated as “T→R”. Along theTIME axis, a sample R→T communication session occurs during a timeinterval 312, and a following sample T→R communication session occursduring a time interval 326. Of course interval 312 is typically of adifferent duration than interval 326—here the durations are shownapproximately equal only for purposes of illustration.

According to blocks 332 and 336, RFID reader 110 talks during interval312, and listens during interval 326. According to blocks 342 and 346,RFID tag 120 listens while reader 110 talks (during interval 312), andtalks while reader 110 listens (during interval 326).

In terms of actual technical behavior, during interval 312, reader 110talks to tag 120 as follows. According to block 352, reader 110transmits wave 112, which was first described in reference to FIG. 1. Atthe same time, according to block 362, tag 120 receives wave 112 andprocesses it, to extract data and so on. Meanwhile, according to block372, tag 120 does not backscatter with its antenna, and according toblock 382, reader 110 has no wave to receive from tag 120.

During interval 326, tag 120 talks to reader 110 as follows. Accordingto block 356, reader 110 transmits a Continuous Wave (CW), which can bethought of as a carrier signal that typically encodes no information. Asdiscussed before, this carrier signal serves both to be harvested by tag120 for its own internal power needs, and also as a wave that tag 120can backscatter. Indeed, during interval 326, according to block 366,tag 120 does not receive a signal for processing. Instead, according toblock 376, tag 120 modulates the CW emitted according to block 356, soas to generate backscatter wave 126. Concurrently, according to block386, reader 110 receives backscatter wave 126 and processes it.

An order, a timing, and other parameters of RFID tag/readercommunications may be defined by industry and/or government protocols(also known as standards). For example, the Class-1 Generation-2 UHFRFID Protocol for Communications at 860 MHz-960 MHz (“Gen2Specification”) by EPCglobal, Inc. is one such industry standard. Thecontents of the Gen2 Specification version 1.2.0 are hereby incorporatedby reference.

FIG. 4 is a block diagram of an RFID reader system 400 according toembodiments. RFID reader system 400 includes a local block 410, andoptionally remote components 470. Local block 410 and remote components470 can be implemented in any number of ways. It will be recognized thatRFID reader 110 of FIG. 1 is the same as local block 410, if remotecomponents 470 are not provided. Alternately, RFID reader 110 can beimplemented instead by RFID reader system 400, of which only the localblock 410 is shown in FIG. 1.

Local block 410 is responsible for communicating with the tags. Localblock 410 includes a block 451 having an antenna and an antenna driverfor communicating with the tags. Some readers, like that shown in localblock 410, contain a single antenna and driver. Some readers containmultiple antennas and drivers and are capable of switching signals amongthem, including sometimes using different antennas for transmitting andfor receiving. Some readers contain multiple antennas and drivers thatcan operate simultaneously. A demodulator/decoder block 453 demodulatesand decodes backscattered signals received from the tags viaantenna/driver block 451. Modulator/encoder block 454 encodes andmodulates an RF signal that is to be transmitted to the tags viaantenna/driver block 451.

In typical embodiments demodulator/decoder block 453 andmodulator/encoder block 454 are operable to demodulate and modulatesignals according to a protocol, such as the Gen2 Specificationmentioned above. In embodiments where multiple demodulators and/ormultiple modulators are present, each may be configured to supportdifferent protocols or different sets of protocols. A protocolspecifies, in part, how symbols are encoded for communication, and mayinclude modulations, encodings, rates, timings, or any other parametersassociated with data communications.

Local block 410 additionally includes an optional local processor 456.Local processor 456 may be implemented in any number of ways known inthe art. Such ways include, by way of examples and not of limitation,digital and/or analog processors such as microprocessors anddigital-signal processors (DSPs); controllers such as microcontrollers;software running in a machine such as a general purpose computer;programmable circuits such as Field Programmable Gate Arrays (FPGAs),Field-Programmable Analog Arrays (FPAAs), Programmable Logic Devices(PLDs), Application Specific Integrated Circuits (ASIC), any combinationof one or more of these; and so on. In some cases, some or all of thedecoding function in block 453, the encoding function in block 454, orboth, may be performed instead by local processor 456. In some caseslocal processor 456 may implement an encryption or authenticationfunction; in some cases one or more of these functions can bedistributed among other blocks such as encoding block 454, or may beentirely incorporated in another block.

Local block 410 additionally includes an optional local memory 457.Local memory 457 may be implemented in any number of ways known in theart. Such ways include, by way of examples and not of limitation,nonvolatile memories (NVM), read-only memories (ROM), random accessmemories (RAM), any combination of one or more of these, and so on.These memories can be implemented separately from local processor 456,or in a single chip with local processor 456, with or without othercomponents. Local memory 457, if provided, can store programs for localprocessor 456 to run, if needed.

In some embodiments, local memory 457 stores data read from tags, ordata to be written to tags, such as Electronic Product Codes (EPCs), TagIdentifiers (TIDs) and other data. Local memory 457 can also includereference data that is to be compared to the EPC codes, instructionsand/or rules for how to encode commands for the tags, modes forcontrolling antenna 451, secret keys, key pairs, and so on. In some ofthese embodiments, local memory 457 is provided as a database.

Some components of local block 410 typically treat the data as analog,such as the antenna/driver block 451. Other components such as localmemory 457 typically treat the data as digital. At some point there is aconversion between analog and digital. Based on where this conversionoccurs, a reader may be characterized as “analog” or “digital”, but mostreaders contain a mix of analog and digital functionality.

If remote components 470 are indeed provided, they are coupled to localblock 410 via an electronic communications network 480. Network 480 canbe a Local Area Network (LAN), a Metropolitan Area Network (MAN), a WideArea Network (WAN), a network of networks such as the internet, or alocal communication link, such as a USB, PCI, and so on. In turn, localblock 410 then includes a local network connection 459 for communicatingwith communications network 480. Communications on the network can besecure, such as if they are encrypted or physically protected, orinsecure if they are not encrypted or otherwise protected.

There can be one or more remote component(s) 470. If there are more thanone, they can be located at the same location, or in differentlocations. They can access each other and local block 410 viacommunications network 480, or via other similar networks, and so on.Accordingly, remote component(s) 470 can use respective remote networkconnections. Only one such remote network connection 479 is shown, whichis similar to local network connection 459, etc.

Remote component(s) 470 can also include a remote processor 476. Remoteprocessor 476 can be made in any way known in the art, such as wasdescribed with reference to local processor 456. Remote processor 476may also implement an authentication function, similar to localprocessor 456.

Remote component(s) 470 can also include a remote memory 477. Remotememory 477 can be made in any way known in the art, such as wasdescribed with reference to local memory 457. Remote memory 477 mayinclude a local database, and a remote database of a StandardsOrganization, such as one that can reference EPCs. Remote memory 477 mayalso contain information associated with command, tag profiles, keys, orthe like, similar to local memory 457.

Of the above-described elements, it may be advantageous to consider acombination of these components, designated as operational processingblock 490. Operational processing block 490 includes the followingcomponents, if present: local processor 456, remote processor 476, localnetwork connection 459, remote network connection 479, and by extensionan applicable portion of communications network 480 that links remotenetwork connection 479 with local network connection 459, which may bedynamically changeable. In addition, operational processing block 490can receive and decode RF waves received via antenna 451, and causeantenna 451 to transmit RF waves according to what it has processed.

Operational processing block 490 includes local processor 456 and/orremote processor 476. If both are provided, remote processor 476 can bemade such that it operates in a way complementary with that of localprocessor 456. In fact, the two can cooperate. It will be appreciatedthat operational processing block 490, as defined this way, is incommunication with both local memory 457 and remote memory 477, if bothare present.

Accordingly, operational processing block 490 is location independent,in that its functions can be implemented either by local processor 456,or by remote processor 476, or by a combination of both. Some of thesefunctions are preferably implemented by local processor 456, and some byremote processor 476. Operational processing block 490 accesses localmemory 457, or remote memory 477, or both for storing and/or retrievingdata.

RFID reader system 400 operates by operational processing block 490generating communications for RFID tags. These communications areultimately transmitted by antenna block 451, with modulator/encoderblock 454 encoding and modulating the information on an RF wave. Thendata is received from the tags via antenna block 451, demodulated anddecoded by demodulator/decoder block 453, and processed by processingoperational processing block 490.

Embodiments of an RFID reader system can be implemented as hardware,software, firmware, or any combination. It is advantageous to considersuch a system as subdivided into components or modules. A person skilledin the art will recognize that some of these components or modules canbe implemented as hardware, some as software, some as firmware, and someas a combination. An example of such a subdivision is now described,together with the RFID tag as an additional module.

FIG. 5 is a block diagram illustrating an overall architecture of anRFID reader 500 according to embodiments. It will be appreciated thatRFID reader 500 is considered subdivided into modules or components.Each of these modules may be implemented by itself, or in combinationwith others. In addition, some of them may be present more than once.Other embodiments may be equivalently subdivided into different modules.It will be recognized that some aspects are parallel with what wasdescribed previously.

An RFID tag 503 is considered here as a module by itself. RFID tag 503conducts a wireless communication 506 with other modules or components,via an air interface 505. It is noteworthy that air interface 505 isreally only a boundary, in that signals or data that pass through it arenot intended to be transformed from one thing to another. Specificationsas to how readers and tags are to communicate with each other, forexample the Gen2 Specification, also properly characterize that boundaryas an interface.

RFID system 500 includes one or more reader antennas 510, and an RFfront-end module 520 for interfacing with reader antenna(s) 510. Thesecan be made as described above.

RFID system 500 also includes a signal-processing module 530. In oneembodiment, signal-processing module 530 exchanges signals with RFfront-end module 520, such as I and Q signal pairs.

RFID system 500 also includes a physical-driver module 540, which isalso known as data-link module. In some embodiments physical-drivermodule 540 exchanges data with signal-processing module 530.Physical-driver module 540 can be the stage associated with the framingof data.

RFID system 500 additionally includes a media access control module 550,which is also known as a MAC layer module. In one embodiment, MAC layermodule 550 exchanges data with physical driver module 540. MAC layermodule 550 can make decisions for sharing the wireless communicationmedium, which in this case is the air interface.

RFID system 500 moreover includes an application-programminglibrary-module 560. This module 560 can include application programminginterfaces (APIs), other objects, etc.

All of these RFID system functionalities can be supported by one or moreprocessors. One of these processors can be considered a host processor.Such a host processor might include a host operating system (OS) and/orcentral processing unit (CPU), as in module 570. In some embodiments,the processor is not considered a separate module, but rather as onethat includes some of the above-mentioned modules of RFID system 500. Insome embodiments the one or more processors perform operationsassociated with retrieving data that may include a tag public key, anelectronic signature, a tag identifier, an item identifier, and asigning-authority public key. In some embodiments the one or moreprocessors verify an electronic signature, create a tag challenge, andverify a tag response.

User interface module 580 may be coupled toapplication-programming-library module 560, for accessing the APIs. Userinterface module 580 can be manual, automatic, or both. It can besupported by the host OS/CPU module 570 mentioned above, or by aseparate processor, etc.

It will be observed that the modules of RFID system 500 form a chain.Adjacent modules in the chain can be coupled by appropriateinstrumentalities for exchanging signals. These instrumentalitiesinclude conductors, buses, interfaces, and so on. Theseinstrumentalities can be local, e.g. to connect modules that arephysically close to each other, or over a network, for remotecommunication.

The chain is used in one direction for transmitting RFID signals and inthe other direction for receiving RFID signals. In transmitting mode,signal initiation can be in any one of the modules. Ultimately, signalsare routed to reader antenna(s) 510 to be transmitted as wireless RFsignals. In receiving mode, reader antenna(s) 510 receives wireless RFsignals, which are in turn processed successively by the various modulesin the chain. Processing can terminate in any one of the modules.

The architecture of RFID system 500 is presented for purposes ofexplanation, and not of limitation. Its particular, subdivision intomodules need not be followed for creating embodiments. Furthermore, thefeatures of the present disclosure can be performed either within asingle one of the modules, or by a combination of modules.

As mentioned previously, embodiments are directed to a synthesized-beamantenna transceiver system that can compensate for beam gain degradationdue to undesired coupling with radiation pattern side lobes and/orfloating antenna elements. Embodiments additionally include programs,and methods of operation of the programs. A program is generally definedas a group of steps or operations leading to a desired result, due tothe nature of the elements in the steps and their sequence. A program isusually advantageously implemented as a sequence of steps or operationsfor a processor, but may be implemented in other processing elementssuch as FPGAs, DSPs, or other devices as described above.

Performing the steps, instructions, or operations of a program requiresmanipulating physical quantities. Usually, though not necessarily, thesequantities may be transferred, combined, compared, and otherwisemanipulated or processed according to the steps or instructions, andthey may also be stored in a computer-readable medium. These quantitiesinclude, for example, electrical, magnetic, and electromagnetic chargesor particles, states of matter, and in the more general case can includethe states of any physical devices or elements. It is convenient attimes, principally for reasons of common usage, to refer to informationrepresented by the states of these quantities as bits, data bits,samples, values, symbols, characters, terms, numbers, or the like. Itshould be borne in mind, however, that all of these and similar termsare associated with the appropriate physical quantities, and that theseterms are merely convenient labels applied to these physical quantities,individually or in groups.

Embodiments further include storage media. Such media, individually orin combination with others, have stored thereon instructions, data,keys, signatures, and other data of a program made according toembodiments. A storage medium according to embodiments is acomputer-readable medium, such as a memory, and is read by a processorof the type mentioned above. If the storage medium is a memory, it canbe implemented in a number of ways, such as Read Only Memory (ROM),Random Access Memory (RAM), etc., some of which are volatile and somenonvolatile.

Even though it is said that the program may be stored in acomputer-readable medium, it should be clear to a person skilled in theart that it need not be a single memory, or even a single machine.Various portions, modules or features of it may reside in separatememories, or even separate machines. The separate machines may beconnected directly, or through a network such as a local access network(LAN) or a global network such as the Internet.

Often, for the sake of convenience only, it is desirable to implementand describe a program as software. The software can be unitary, orthought of in terms of various interconnected distinct software modules.

FIG. 6 is a block diagram illustrating an architecture 600 for aninterface converter according to embodiments. Architecture 600 includesa utility 640, which is a mechanism for performing some or all of thereader features described above.

More particularly, utility 640 may cause a tag to store one or morereceived instructions in its memory, execute the instructions inresponse to a subsequent command or trigger event, and responddifferently to a reader command based on results generated by executingthe instructions.

Architecture 600 additionally includes an interface converter 650 and anagent 660. Embodiments also include methods of operation of interfaceconverter 650. Interface converter 650 enables agent 660 to controlutility 640. Interface converter 650 is so named because it performs aconversion or a change, as will be described in more detail below. Agent660, interface converter 650, and utility 640 can be implemented in anyway known in the art. For example, each can be implemented in hardware,middleware, firmware, software, or any combination thereof. In someembodiments, agent 660 is a human.

Between interface converter 650, agent 660 and utility 640 there arerespective boundaries 655 and 645. Boundaries 655 and 645 are properlycalled interfaces, in that they are pure boundaries, similar to theabove described air interface.

In addition, it is a sometimes informal usage to call the space betweenboundaries 655 and 645, which includes interface converter 650, an“interface” 656. Further, it is common to designate this space with adouble arrow as shown, with an understanding that operations take placewithin the arrow. So, although “interface” 656 is located at a boundarybetween agent 660 and utility 640, it is not itself a pure boundary.Regardless, the usage of “interface” 656 is so common for interfaceconverter 650 that this document sometimes also refers to it as aninterface. It is clear that embodiments of such an “interface” 656 canbe included in this invention, if they include an interface converterthat converts or alters one type of transmission or data to another, aswill be seen below.

Agent 660 can be one or more layers in an architecture. For example,agent 660 can be something that a programmer programs. In alternativeembodiments, where agent 660 is a human, interface converter 650 caninclude a screen, a keyboard, or any other user interface.

FIG. 7 is a sample screenshot 750 associated with an interface for aninterface converter, such as the interface converter 650 of FIG. 6.Screenshot 750 can be that of a computer screen for a human agent,according to an embodiment. What is displayed in screenshot 750 exposesthe functionality of a utility, such as utility 640. Inputs by the uservia a keyboard, a mouse, etc., can ultimately control utility 640.Accordingly, such inputs are received in the context of screenshot 750.These inputs are determined from what is needed for controlling andoperating utility 640. An advantage with such interfacing is that agent660 can prepare RFID applications at a higher level, without needing toknow how to control lower level RFID operations. Such lower level RFIDoperations can be as described in the Gen2 Specification, incryptographic algorithms, in other lower level protocols, etc. Utility640 can be controlled in any number of ways. Some such ways are nowdescribed.

Returning to FIG. 6, one way interface converter 650 can be implementedis as a software Application Programming Interface (API). This API can,for example, control or provide inputs to an underlying softwarelibrary.

Communications can be made between agent 660, interface converter 650,and utility 640. Such communications can be as input or can beconverted, using appropriate protocols, etc. These communications canencode commands, data, etc., and can include any one or a combination ofthe following: a high-down communication HDNT from agent 660 tointerface converter 650; a low-down communication LDNT from interfaceconverter 650 to utility 640; a low-up communication LUPT from utility640 to interface converter 650; and a high-up communication HUPT frominterface converter 650 to agent 660. These communications can bespontaneous, or in response to another communication, or in response toan input or an interrupt, etc.

Commands are more usually included in communications HDNT and LDNT, forultimately controlling utility 640. Controlling can be in a number ofmanners. One such manner can be to install utility 640, or just afeature of it. Such installing can be by spawning, downloading, etc.Other such manners can be to configure, enable, disable, or operateutility 640, or just a feature of it. These commands can be standalone,or can carry parameters, such as data, instructions to be stored bytags, etc. In some embodiments interface converter 650 can convert thesecommands to a format suitable for utility 640.

Data is more usually included in communications HUPT and LUPT. The datacan inform as to success or failure of executing an operation. The datacan also include tag data, which can be both codes read from tags anddata about reading tags (such as time stamps, date stamps, etc.). Insome embodiments interface converter 650 can convert the data to aformat suitable for agent 660, including in some cases aggregating,filtering, merging, or otherwise altering the format or utility of thedata.

It should be noted that what passes across a single pure boundary isunchanged (by the mere definition of a pure boundary). But what passesthrough interface converter 650 can be changed or not. Moreparticularly, high-down communication HDNT can be encoded similarly to,or differently from, low-down communication LDNT. In addition, low-upcommunication LUPT can be encoded similarly to, or differently from,high-up communication HUPT. When encodings are different, the differencecan be attributed to interface converter 650, which performs a suitablechange, or conversion, of one communication to another. The change, orconversion, performed by interface converter 650 is for exposing thefunctionality of utility 640 to agent 660, and vice versa. In someembodiments, a command is converted, but a parameter is passed alongwithout being converted. What is not converted at one module may beconverted at another. Such modules taken together can also form aninterface converter according to embodiments.

Agent 660, interface converter 650, and utility 640 can be implementedas part of a reader, or as a different device. When implemented as partof a reader, FIG. 8 suggests a scheme 800 where agent 660, interfaceconverter 650, and utility 640 can be implemented in connection withrespective reader modules that are suitable, depending on therequirements.

FIG. 9 depicts a perspective view of a synthesized-beam antenna (SBA)900 according to embodiments. SBA 900 includes an array of multipleantenna elements 902 and 904 arranged along an antenna plane, and anantenna ground plane 908 that lies behind the antenna elements 902 and904. Each antenna element has a radiating direction vector 906 (onlyshown for one antenna element) that is perpendicular to the antennaplane. An RF radiation pattern (or “beam”) for receiving or transmittingan RF signal can be synthesized by driving or activating one or more ofthe antenna elements 902 and 904. The direction of the synthesized RFbeam (represented by the direction of the beam's primary lobe—the lobehaving the highest radiated power) can be controlled by selecting theparticular antenna elements that are activated and the particularwaveforms used to drive those elements. An antenna element is activatedor driven when it is electrically connected to an RF input or output(e.g., a transmitter output, a receive input, a transceiverinput/output, or any suitable RF component). For example, an antennaelement is activated/driven if it is used to transmit or receive asignal.

Two components are said to be electrically connected when alow-impedance path exists between them, and are said to be disconnectedif no such low-impedance path exists. Of course, electricallydisconnected components will generally have some unavoidable straycapacitive or inductive coupling between them, but the intent of thedisconnection is to minimize this stray coupling to a negligible levelwhen compared with an electrically connected path. In some embodiments,antenna elements include one or more of patch antennas, slot antennas,wire antennas, horn antennas, and helical antennas. While SBA 900 onlyincludes nine antenna elements, antenna arrays with any number ofantenna elements may be used. Also, in some embodiments the antennaground plane 908 may actually be a surface that is at least partlynonplanar (e.g., curved, concave, convex, etc.).

FIGS. 10A and 10B depict the directions of potential RF beams that canbe synthesized by an SBA 1000 similar to SBA 900 in FIG. 9. SBA 1000 hasnine antenna elements 1002-1018, with element 1002 residing at thecenter and elements 1004-1018 positioned around it. If two or moreantenna elements arranged in a line are activated to synthesize an RFbeam, the synthesized beam can be steered (i.e., its direction can becontrolled or changed) along a plane that includes both the radiatingdirection vectors for the individual antenna elements and the line theantenna elements are arranged in. For example, if antenna elements 1002,1004, and 1012 are activated, an RF beam can be synthesized and steeredalong a plane 1026 that includes the radiating direction vectors forantenna elements 1002, 1004, and 1012 and the line between the elements.Similarly, the RF beam synthesized by driving elements 1002, 1006, and1014 can be steered along plane 1020; the beam synthesized by elements1002, 1008, and 1016 can be steered along plane 1022; and the beamsynthesized by elements 1002, 1010, and 1018 can be steered along plane1024.

FIG. 10B shows how an RF beam synthesized by activating antenna elementslocated along plane 1020 can be steered, with the diagram to the leftdepicting a head-on view similar to FIG. 10A and the diagram to theright depicting a side view. The direction of a synthesized beam can becontrolled by varying the amount of phase-shifting that is applied tothe waveforms supplied to the activated antenna elements. When all threeelements are driven with the same waveform, an RF beam 1032 issynthesized with a direction parallel to the radiating direction vectorsof the individual antenna elements. If the waveforms supplied to the topelement (e.g., element 1006 in FIG. 10A) and the bottom element (e.g.,element 1014 in FIG. 10A) are phase-shifted to lag behind and lead,respectively, the waveform supplied to the middle element (e.g., element1002 in FIG. 10A), RF beam 1030 can be synthesized, pointing upward withrespect to beam 1032. Similarly, if the phase-shifting is reversed(i.e., the top element receives the leading waveform and the bottomelement receives the lagging waveform), RF beam 1034 can be synthesized,pointing downward with respect to beam 1032. Synthesized beam directionmay also be controlled by adjusting the relative amplitudes of thewaveforms supplied to the different antenna elements.

While FIG. 10B describes RF beams synthesized by antenna elementsarranged in a single line (or plane), in some embodiments one or moreadditional antenna elements may be activated to synthesize an RF beam.For example, an RF beam may be synthesized by activating antennaelements located along plane 1020 as well as antenna elements 1010and/or 1018, which are not located along plane 1020. Activating theseadditional antenna elements may allow for additional RF beam shaping,for example to narrow the synthesized RF beam.

FIG. 11 depicts a synthesized-beam transceiver system 1100 with afixed-power transceiver 1102, which in some embodiments may be similarto RFID reader 110 (FIG. 1), and a synthesized-beam antenna 1104 similarto SBA 1000 in FIG. 10. Fixed-power transceiver 1102 supplies conductedpower in the form of phase-shifted and unshifted waveforms to activatedantenna elements in the synthesized-beam antenna 1104 in order tosynthesize an RF beam. Generally, the fixed-power transceiver 1102 iscalibrated to cause the synthesized beam antenna 1104 to synthesize anRF beam 1106 with a particular desired peak radiated power. Inembodiments where the transceiver system is an RFID reader system, thetag read/write capabilities of a reader are directly related to theradiated power of the RF beam. Therefore, synthesized RF beams withpower near or at the maximum allowed radiated power limit 1112 may bedesirable. However, as the synthesized RF beam is steered to point awayfrom the antenna element direction vectors (which are orientedvertically downward in the case of FIG. 11), the beam power decreasesdue to the finite beamwidth of the antenna elements. This results inundesirable power gaps 1114/1116 between the low-gain, off-axissynthesized beams 1108 and 1110 and the radiated power limit 1112,resulting in reduced tag read/write capabilities.

FIG. 12 depicts a synthesized-beam transceiver system 1200 capable ofcompensating for beam gain variations according to embodiments. Thetransceiver system 1200 includes a compensating variable-powertransceiver 1202 coupled to a synthesized-beam antenna 1204, similar toantenna 1104 (FIG. 11) and SBA 1000 (FIG. 10). As with the fixed-powertransceiver system 1100 described in FIG. 11, RF beam 1206 (analogous tobeam 1106 in FIG. 11) can be synthesized with a desired power near or atthe radiated power limit 1212. However, in contrast to the fixed-powertransceiver 1102 in transceiver system 1100, the compensatingvariable-power transceiver 1202 in system 1200 can compensate for powerlosses in off-axis beams by varying the conducted power supplied to thesynthesized beam antenna 1204. Therefore, the system 1200 can synthesizecompensated off-axis beams 1208 and 1210 such that power gaps arereduced, if not eliminated.

In some embodiments, transceiver system 1200 may be an RFID readersystem, although the synthesized-beam gain compensation techniquesdescribed herein may be used in non-RFID applications. FIG. 13 is ablock diagram of such an RFID synthesized-beam reader system 1300according to one embodiment. Reader system 1300 includes a compensatingvariable-power reader 1302 and a synthesized-beam antenna 1320, similarto transceiver 1202 and antenna 1204 in FIG. 12, respectively. Reader1302 includes a controller 1304, a transmitter 1306 (which itselfincludes a transmit subassembly 1308 and a variable gain adjust 1310), areceiver 1314, a duplexer 1312 (which allows the reader 1302 to bothtransmit and receive), and a memory 1322. Controller 1304, which mayinclude one or more processors, is configured to cause reader system1300 to synthesize RF beams and to adjust the conducted power output byreader 1302 in order to compensate for beam gain variations. In someembodiments, controller 1304 adjusts the reader output power based ontransmit power settings (e.g., transmit power data 1324) stored inmemory 1322.

Transmit power data 1324 may include settings for transmitter 1306,variable gain adjust 1310, receiver 1314, and/or synthesized-beamantenna 1320. In particular, transmit power data 1324 may indicate theappropriate settings for variable gain adjust 1310 and/or receiver 1314for particular RF beam orientations in order to achieve a desired beampower. Transmit power data 1324 may be pre-stored in memory 1322 (e.g.,as a result of testing and calibration at the time ofmanufacture/testing), or may be dynamically stored or updated bycontroller 1304 during operation of reader system 1300.

For example, when synthesizing an RF beam, controller 1304 may transmita beam select signal 1328 to synthesized-beam antenna 1320 to activateor drive the particular antenna elements in antenna 1320 used tosynthesize the beam. Controller 1304 may also retrieve transmit powerdata 1324 that corresponds to the desired RF beam orientation frommemory 1322, determine a transmit power select signal 1326 from theretrieved transmit power data 1324, and then adjust variable gain adjust1310 based on the determined transmit power select signal 1326. In someembodiments, controller 1304 also adjusts receiver 1314 based on theretrieved transmit power data 1324. Controller 1304 may also adjust oneor more of an amplifier gain, an amplifier bias, a digital-to-analogconverter (DAC) gain, and a DAC input in order to adjust the conductedpower.

FIG. 14 is a block diagram of an RFID synthesized-beam reader system1400 according to another embodiment. Reader system 1400 is similar toreader system 1300 described in FIG. 13, with similarly-numberedelements operating similarly. Controller 1404 is similar to controller1304 in that it is configured to cause reader system 1400 to synthesizeRF beams, and to control the output power of reader 1402 in order tocompensate for beam gain variations. However, controller 1404 directlyreceives sensed beam power data (sensor transmission power data 1424)from a power sensor 1422 associated with synthesized beam antenna 1320.Based on the received sensor transmission power data, controller 1404then determines and adjusts settings for variable gain adjust 1310and/or receiver 1314 that result in the desired beam power.

While reader systems 1300 and 1400 control reader output power based oninformation received from different components of the system (e.g.,receiving data from memory 1322 or power sensor 1422), in someembodiments a reader system may include both a memory similar to memory1322 and a power sensor similar to power sensor 1422. Transmit powerdata may be pre-stored in the memory, for example at the time ofmanufacture or testing, and a controller similar to controllers1304/1404 may use the stored transmit power data to adjust the readersystem transmitter/receiver initially. The controller may then usesensed transmit power data from the power sensor to further adjust thetransmitter/receiver, and then may update the transmit power data storedin the memory with data received from the power sensor. In someembodiments, the reader system may receive power data from an externaldevice or location. For example, the reader system may retrieve transmitpower data from a remote location, such as a server, that is remotelyaccessible by the reader via, e.g., one or more networks. In someembodiments, the reader system may receive sensed power data fromexternal devices (e.g., an RFID tag, a different reader, an externalsensor, etc.).

FIG. 15 is a flowchart depicting a synthesized-beam gain compensationprocess 1500 according to embodiments. Process 1500 begins at step 1502,where a transceiver controller (e.g., reader controller 1304/1404)determines if the state of a synthesized RF beam for transmitting orreceiving an RF signal has changed. For example, the transceiver systemmay have been commanded to synthesize an RF beam, or it may have beencommanded to change the orientation of a synthesized beam. A beam statechange may also include a change in expected beam power. For example,the transceiver controller may determine that beam power is lower orhigher than desired based on sensed transmit power data (e.g., frompower sensor 1422).

If there is no beam state change, then process 1500 loops back to step1502. If there is a beam state change, then process 1500 moves to step1504, where the transceiver controller determines a new power value forthe transceiver (e.g., a new transmit power select 1326). The controllermay determine the new power value based on stored transmit powersettings (e.g., transmit power data 1324), sensed transmit power (e.g.,sensor transmit power data 1424), or a combination of the two. Thecontroller then adjusts the transceiver conducted power in step 1506,then returns to step 1502 to monitor for beam state changes.

Other factors may also cause synthesized-beam gain degradation. FIG. 16depicts a synthesized-beam transceiver system 1600 with beam patternvariations due to antenna element coupling. Transceiver system 1600 issimilar to transceiver system 1100, with fixed-power transceiver 1602similar to fixed-power transceiver 1102 and synthesized-beam antenna1604 similar to antenna 1104. When transceiver system 1600 is commandedto synthesize a particular RF beam with a particular direction (e.g.,expected beam 1606), in general not all of the antenna elements on SBA1604 are activated or driven. Antenna elements that are notactivated/driven may float (i.e., lack a low-impedance path to an RFinput/output or a fixed potential), thereby coupling (electricallyand/or magnetically) with active antenna elements. This coupling mayresult in a beam pattern 1608 different from the expected beam 1606 andpotentially having an undesired shape and/or degraded peak radiatedpower.

FIG. 17 is a block diagram of a synthesized-beam antenna steering system1700 according to embodiments. Antenna steering system 1700 may be partof the synthesized-beam antenna (e.g., SBA 1204, 1320, 1604), part ofthe transceiver (e.g., reader 1302), or an entirely different module.The antenna steering system 1700 is coupled to antenna elements1002-1018, and includes an RF input/output 1702, a phase shifter 1704, aphase shifter control 1714, antenna element switches 1706 and 1710, andswitch controls 1708 and 1712. Phase shifter control 1714 and switchcontrols 1708 and 1712 receive control signals from a transceivercontroller (e.g., reader controller 1304/1404) to synthesize RF beams.For example, if beam 1030 (shown in FIG. 10B) is to be synthesized, thecontroller directs switch controls 1708 and 1712 to adjust switches 1706and 1710 to connect antenna element 2 (1006) and element 6 (1014) tophase shifter 1704. The controller also directs phase shifter control1714 (and phase shifter 1704) to apply the appropriate phase shifts tothe signals provided to the antenna elements.

As discussed above, antenna elements that are not driven or activatedmay couple with a synthesized beam, which may result in the beam havingan unacceptable pattern or gain. In some embodiments, unused (i.e.,unactivated or not driven) antenna elements may be terminated orelectrically connected to a reference potential to prevent undesiredcoupling. For example, unused antenna elements may be connected to aparticular DC bias, chassis ground (e.g., an antenna or reader housingor an antenna ground plane such as ground plane 908 in FIG. 9), earthground, or any other suitable reference potential to prevent coupling.In some embodiments, the reference potential may also be used as areturn for the activated/driven antenna elements. FIG. 18A is a blockdiagram depicting details of a synthesized-beam antenna elementtermination system 1800 according to embodiments. While terminationsystem 1800 only depicts two antenna elements 1804 and 1806, more thantwo antenna elements in a synthesized-beam antenna may be terminated asdepicted.

Termination system 1800 includes a switch 1808 (similar to switches 1706and 1710 in FIG. 17) that electrically connects antenna element 1804 orantenna element 1806 to the RF input/output 1802 of the transceiver.Each antenna element is also electrically connected to a referencepotential (1818/1820) via a low-impedance path (1810/1812) and a shuntswitch (1814/1816), forming a low-impedance termination. In someembodiments, the low-impedance terminations are formed as close to theantenna feed points as possible. The shunt switches 1814 and 1816 may becontrolled by a transceiver controller (e.g., reader controllers1304/1404 in FIGS. 13 and 14) or a controller in the synthesized-beamantenna. When an antenna element is being used to synthesize a beam totransmit or receive a signal (i.e. is activated), its correspondingshunt switch disconnects it from the reference potential. For example,element 1804 is being used to synthesize a beam (as indicated by theposition of switch 1808), and its shunt switch 1814 disconnects itslow-impedance path 1810 from reference potential 1818. In contrast, whenan antenna element is not being used to synthesize a beam (e.g., element1806) its shunt switch (switch 1816) connects the low-impedance path1812 to reference potential 1820. Thus, unused antenna element 1806 isshunted (i.e., electrically connected) to a reference potential via alow-impedance path and will not couple to the synthesized RF beam.

Antenna elements may also be terminated without shunt switches byappropriate line impedance design. FIG. 18B is a block diagram depictingdetails of a synthesized-beam antenna element termination system 1830without shunt switches according to embodiments. Similar to terminationsystem 1800, termination system 1830 includes antenna elements 1804 and1806 and switch 1808 that either connects antenna element 1804 orantenna element 1806 to the transceiver RF input/output 1802.Termination system 1830 also includes lines 1832 and 1834 that connectthe terminals of switch 1808 to antenna elements 1804 and 1806. Thelines are designed to have low open-circuit impedances such thatconnected antenna elements are electrically connected to a referencepotential when they are disconnected from the transceiver RFinput/output. For example, line 1834 is designed to have a low impedancewhen switch 1808 does not connect transceiver RF input/output 1802 toantenna element 1806.

As described above, the impedances of lines 1832 and 1834 whendisconnected from transceiver input/output 1802 (their “open-circuitimpedances”) can be designed to be low at the transceiver operatingfrequencies in order to electrically connect antenna elements to areference potential such as chassis ground, earth ground, or any othersuitable potential. Line impedance is based on line length, thedielectric constant of the material the line is fabricated upon, and thefrequency of the RF signals driving the antenna elements (i.e., thetransceiver operating frequencies). Therefore, when lines 1832 and 1834have lengths that satisfy the relation

${length} = {\left( {{2\; n} + 1} \right)*\frac{\lambda}{4}}$where n is a real, nonnegative integer (e.g., 0, 1, 2, 3, . . . ) and λis the wavelength (itself determined via the relation

${= \frac{c}{f*\sqrt{ɛ_{r}}}},$where c is the speed of light, f is the transceiver operating frequency,and ∈_(r) is the dielectric constant of the material the line isfabricated upon), they will have low open-circuit impedances at thetransceiver operating frequency, which allow their associated antennaelements to be electrically connected to a reference potential (e.g.,ground).

FIG. 18C is a block diagram depicting details of a synthesized-beamantenna element termination system 1840 with shunt switches and compleximpedance paths according to embodiments. Similar to termination systems1800 and 1830, termination system 1840 includes antenna elements 1804and 1806 and switch 1808 that electrically connects either antennaelement 1804 or antenna element 1806 to transceiver RF input/output1802. Similar to termination system 1800, system 1840 includes switches(1850 and 1852) that electrically connect antenna elements 1804 and 1806to reference potentials 1854 and 1856. Termination system 1840 alsoincludes complex impedances 1842 and 1846, each of which electricallyconnect an antenna element (1804/1806) to a reference potential(1854/1856) when the associated switch (1850/1852) is closed. Compleximpedances 1842 and 1846 are represented by resistive (R), inductive(+jX), and capacitive (−jX) constituent impedances. By selectingappropriate values for complex impedances 1842/1846 and the line lengths1844/1848, a low-impedance path can be provided between each antennaelement and reference potential.

FIG. 19 is a flowchart depicting a steering and termination process 1900for a synthesized-beam transceiver system (e.g., a synthesized-beamreader system) according to embodiments. Process 1900 begins at step1902, where the transceiver system receives instructions to steer orsynthesize a first RF beam oriented in a first direction (e.g., in thedirection of beam 1030 in FIG. 10B) for transmitting or receiving asignal. In step 1904, the transceiver system determines the particularantenna elements that must be activated or driven to synthesize thefirst beam, which in some embodiments are the antenna elements on afirst axis (e.g., elements 1002, 1006, and 1014 for axis 1020 in FIG.10A), and proceeds to activate those elements and simultaneouslyterminate (i.e., shunt to a reference potential) at least one otherinactive antenna element (e.g., at least one of elements 1004,1008-1012, and 1016-1018 in FIG. 10).

Subsequently, the transceiver system receives instructions in step 1906to synthesize a second RF beam oriented in a second direction differentfrom the first direction. The transceiver system then determines in step1908 if new antenna elements should be activated (or deactivated) tosynthesize the second beam. For example, if the second direction lies onthe plane associated with the first axis (e.g., the direction of beam1034 in FIG. 10B), then the transceiver system may not need to activatenew elements, and instead may adjust the phase differences of thewaveforms provided to the activated elements. However, in someembodiments, if off-axis elements are activated (e.g., to assist inbeam-shaping), then new elements may need to be activated or deactivatedeven if the second direction is on the plane associated with the firstaxis. If the system determines that new elements should be activated ordeactivated, it proceeds to activate and deactivate those elements andto further terminate newly deactivated elements.

In some embodiments, steering and termination process 1900 may becombined with the synthesized-beam gain compensation process 1500described in FIG. 15. For example, a synthesized-beam transceiver systemmay both terminate unused, inactive antenna elements and adjustconducted power to achieve a desired beam power or shape.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams and/orexamples. Insofar as such block diagrams and/or examples contain one ormore functions and/or aspects, it will be understood by those within theart that each function and/or aspect within such block diagrams orexamples may be implemented, according to embodiments formed,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. For example, transceivers in thisdisclosure are interchangeable with RFID readers, and vice-versa.Functionally equivalent methods and apparatuses within the scope of thedisclosure, in addition to those enumerated herein, will be apparent tothose skilled in the art from the foregoing descriptions. Suchmodifications and variations are intended to fall within the scope ofthe appended claims. The present disclosure is to be limited only by theterms of the appended claims, along with the full scope of equivalentsto which such claims are entitled. It is to be understood that thisdisclosure is not limited to particular methods, configurations,antennas, transmission lines, and the like, which can, of course, vary.It is also to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto be limiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood that if a specific number of anintroduced claim recitation is intended, such an intent will beexplicitly recited in the claim, and in the absence of such recitationno such intent is present. For example, as an aid to understanding, thefollowing appended claims may contain usage of the introductory phrases“at least one” and “one or more” to introduce claim recitations.However, the use of such phrases should not be construed to imply thatthe introduction of a claim recitation by the indefinite articles “a” or“an” limits any particular claim containing such introduced claimrecitation to embodiments containing only one such recitation, even whenthe same claim includes the introductory phrases “one or more” or “atleast one” and indefinite articles such as “a” or “an” (e.g., “a” and/or“an” should be interpreted to mean “at least one” or “one or more”); thesame holds true for the use of definite articles used to introduce claimrecitations. In addition, even if a specific number of an introducedclaim recitation is explicitly recited, those skilled in the art willrecognize that such recitation should be interpreted to mean at leastthe recited number (e.g., the bare recitation of “two recitations,”without other modifiers, means at least two recitations, or two or morerecitations).

Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, and C”would include but not be limited to systems that have A alone, B alone,C alone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). Where a convention analogous to “at least oneof A, B, or C, etc.” is used, in general such a construction is intendedin the sense one having skill in the art would understand the convention(e.g., “a system having at least one of A, B, or C” would include butnot be limited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc.). It will be further understood that virtually anydisjunctive word and/or phrase presenting two or more alternative terms,whether in the description, claims, or drawings, should be understood tocontemplate the possibilities of including one of the terms, either ofthe terms, or both terms. For example, the phrase “A or B” will beunderstood to include the possibilities of “A” or “B” or “A and B.”

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember.

We claim:
 1. A method for steering a beam of a two-dimensional array ofantenna elements, the method comprising: activating a first subset ofthe elements to orient the beam in a first direction; shunting RF energycoupled to at least one element not in the first subset by electricallyconnecting the at least one element not in the first subset to areference potential, wherein electrically connecting at least oneelement not in the first subset to the reference potential includeselectrically connecting all elements adjacent to the elements in thefirst subset to the reference potential; and subsequently, activating asecond subset of the elements to orient the beam in a second directiondifferent from the first direction, and shunting RF energy coupled to atleast one element not in the second subset by electrically connectingthe at least one element not in the second subset to the referencepotential.
 2. The method of claim 1, wherein the first subset ofelements is on a first axis.
 3. The method of claim 1, wherein the atleast one element not in the first subset is in the second subset. 4.The method of claim 1, wherein the reference potential is at least oneof an antenna ground plane, chassis ground, and earth ground.
 5. Themethod of claim 1, wherein the reference potential is used as a returnfor the activated elements.
 6. A two-dimensional antenna array forsynthesizing a steerable beam, comprising: a plurality of antennaelements, and processing circuitry configured to activate a first subsetof the elements to orient the beam in a first direction; shunting RFenergy coupled to at least one element not in the first subset byelectrically connecting the at least one element not in the first subsetto a reference potential, wherein electrically connecting at least oneelement not in the first subset to the reference potential includeselectrically connecting all elements adjacent to the elements in thefirst subset to the reference potential; subsequently, activate a secondsubset of the elements to orient the beam in a second directiondifferent from the first direction, and shunting RF energy coupled to atleast one element not in the second subset by electrically connectingthe at least one element not in the second subset to the referencepotential.
 7. The array of claim 6, wherein the first subset of elementsis on a first axis.
 8. The array of claim 6, wherein the at least oneelement not in the first subset is in the second subset.
 9. The array ofclaim 6, wherein the reference potential is at least one of an antennaground plane, chassis ground, and earth ground.
 10. A method fororienting a beam of a two-dimensional array of antenna elements, themethod comprising: activating a first subset of the elements to orientthe beam in a first direction; shunting RF energy coupled to at leastone inactive element not in the first subset by electrically connectingthe at least one inactive element to a reference potential, whereinelectrically connecting at least one inactive element includeselectrically connecting all inactive elements adjacent to the activatedelements to the reference potential; subsequently, activating a secondsubset of the elements to orient the beam in a second directiondifferent from the first direction, and shunting RF energy coupled to atleast one inactive element not in the second subset by electricallyconnecting the at least one inactive element to the reference potential.11. The method of claim 10, wherein an inactive element is subsequentlyan activated element.
 12. The method of claim 10, wherein the referencepotential is at least one of an antenna ground plane, chassis ground,and earth ground.
 13. The method of claim 10, wherein the referencepotential is used as a return for the activated elements.
 14. Atwo-dimensional antenna array for synthesizing a steerable beam,comprising: a plurality of antenna elements, and processing circuitryconfigured to activate a first subset of the elements to orient the beamin a first direction; shunting RF energy coupled to at least oneinactive element not in the first subset by electrically connecting atthe east one inactive element to a reference potential, whereinelectrically connecting at least one inactive element to the referencepotential includes electrically connecting all inactive elementsadjacent to the activated elements to the reference potential;subsequently, activate a second subset of the elements to orient thebeam in a second direction different from the first direction, andshunting RF energy coupled to at least one inactive element not in thesecond subset by electrically connecting the at least one inactiveelement to the reference potential of the antenna array.
 15. The arrayof claim 14, wherein an inactive element is subsequently an activatedelement.
 16. The array of claim 14, wherein the reference potential isat least one of an antenna ground plane, chassis ground, and earthground.